kes Add some additional locking in the cats directory in subroutines

kes  Add some additional locking in the cats directory in subroutines
     that modify packet variables called from batch insert.
kes  Rework how dcrs are allocated. new_dcr() can now be called
     with an existing pointer, and it will simply clean it up.
     This allows the reservation system to test various different
     devices, and will permit easy device changes.
kes  A bunch of changes all over to handle new new_dcr() calling
     sequence.
kes  Work more on the Volume management in the SD. Remember Volumes
     for tape drives and for autochangers (even virtual disk changers).
kes  When looking at the Volume list to reserve a drive, handle
     autochanger names correctly by interating through the changer
     devices.  Also call the Director to see if a Volume is suitable
     for the current job.
kes  Fix some bugs in bscan. Make sure all media records are written.
     Make sure that valid JobMedia records are written for disk files.
     Previously they were completely wrong.

git-svn-id: https://bacula.svn.sourceforge.net/svnroot/bacula/trunk@5038 91ce42f0-d328-0410-95d8-f526ca767f89